As to the substrate-holding container for use in transportation and safekeeping of substrates, there are known and rendered to actual use, heretofore, substrate-holding containers, as described in the official publication of Japanese Utility Model Kokai No. 1-51058, constituted of a carrier having holding grooves to support a plurality of substrates at oppositely facing positions, a body of the substrate-holding container to hold the same and a covering capable of being opened and closed as fittingly engaged with the body of the substrate-holding container along the outer periphery thereof as well as presser members to stably fix the substrates, a gasket member held by sandwiching between the body of the substrate-holding container and the covering around the outer peripheries thereof, and others.
In these substrate-holding containers, there are used, heretofore, synthetic resinous materials such as, for example, polypropylene, polyethylene, polycarbonate, polybutylene terephthalate and the like in respect of their good balance of lightness in weight, moldability and so on in accordance with the requirements for properties of the respective constituent parts.
Among these constituent parts, the gasket member is, usually, held by sandwiching within the fitting-engagement space between the body of the substrate-holding container and the covering around the outer peripheries and serves to isolate the inside and outside ambiences of the substrate-holding container by the resilient compression due to fitting engagement of the body of the substrate-holding container and the covering so as to prevent intrusion of contaminant substances of mainly particles from outside of the substrate-holding container during safekeeping or transportation. Furthermore, advantageous effects can be obtained by the gasket member that, in transportation on an aircraft, pressure changes within the substrate-holding container due to changes of the external pressure can be mitigated consequently preventing intrusion of particles into the substrate-holding container and movement of particles in the substrate-holding container due to movement of the air flow so as to decrease contamination of the substrates contained.
As is described above, the gasket member is required to have properties that it is deformed by elastic compression thereby to assuredly keep the air-tight sealed condition but still regains the original shape when the pressure is removed by opening the covering so that it should essentially have appropriate rubber elasticity and surface hardness. As a material to satisfy the requirement for the surface hardness, there have been used heretofore those thermoplastic elastomer materials f relatively high flexibility by compounding a polystyrene, polyolefin and the like as the base resin with an external softening agent such as a paraffin oil as a typical one in order to adjust the surface hardness thereof.
These softening agents, however, generally never form chemical bondings with the base resin but are in a condition of mere physical blending so that they are liable to cause bleeding to the surface or emission of gaseous organic matters by dissipation, vaporization and so on due to various factors encountered in the molding conditions and use ambience of the gasket. An issue coming up as a problem is that degradation of the resinous material used as the base resin not only causes enhancement of the above possibility but also increases the emitted amount of the gases generated from the material per se consequently resulting in an influence of contamination occurring on the substrates caused by these organic matters.
In view of the situations as above, the problem in the present invention is to provide a gasket member for substrate-holding containers, with a principal target being to decrease contamination of the substrate materials contained by organic matters as low as possible with little dissipation and emission of organic matters, which has flexibility sufficient to ensure sealability of the substrate-holding container without decreasing the operability of the covering in opening and closing.